Message-Id: <20250723-drm-bridge-alloc-getput-for_each_bridge-v1-0-be8f4ae006e9@bootlin.com>
Date: Wed, 23 Jul 2025 11:54:07 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Miguel Ojeda <ojeda@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, 
 Chaoyi Chen <chaoyi.chen@...k-chips.com>, Hui Pu <Hui.Pu@...ealthcare.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: [PATCH 0/9] drm/bridge: get/put the bridge when looping over the
 encoder chain

This series adds drm_bridge_get/put() calls for DRM bridges used when
looping over bridges in an encoder chain.

This is part of the work towards removal of bridges from a still existing
DRM pipeline without use-after-free. The grand plan was discussed in [1].
Here's the work breakdown (➜ marks the current series):

 1. ➜ add refcounting to DRM bridges (struct drm_bridge)
    (based on devm_drm_bridge_alloc() [0])
    A. ✔ add new alloc API and refcounting (in v6.16-rc1)
    B. ✔ convert all bridge drivers to new API (now in drm-misc-next)
    C. ✔ kunit tests (now in drm-misc-next)
    D. ✔ add get/put to drm_bridge_add/remove() + attach/detach()
         and warn on old allocation pattern (now in drm-misc-next)
    E. ➜ add get/put on drm_bridge accessors
       1. ✔ drm_bridge_chain_get_first_bridge() + add a cleanup action
       2. … drm_bridge_get_prev_bridge()
       3. … drm_bridge_get_next_bridge()
       4. ➜ drm_for_each_bridge_in_chain()
       5. drm_bridge_connector_init
       6. of_drm_find_bridge
       7. drm_of_find_panel_or_bridge, *_of_get_bridge
    F. debugfs improvements
 2. handle gracefully atomic updates during bridge removal
 3. … avoid DSI host drivers to have dangling pointers to DSI devices
 4. finish the hotplug bridge work, removing the "always-disconnected"
    connector, moving code to the core and potentially removing the
    hotplug-bridge itself (this needs to be clarified as points 1-3 are
    developed)

Most loops are based on drm_for_each_bridge_in_chain(), so add a scoped
variant that does not use an externally-declared iterator variable and
ensures that a reference to the bridge pointed to by the iterator is
taken/released before/after every iteration (and when breaking out of the
loop).

All conversions are trivial except for drm_bridge_connector_init() which
needs some preliminary cleanups (patches 1-2).

omapdrm/omap_encoder.c is the only driver iterating over the encoder bridge
chain starting from a specific bridge, instead of iterating over the whole
list. For this use case, add a drm_for_each_bridge_in_chain_from() variant.

This series depends on two fixes to bridge-connector:

 * commit 103578241512 ("drm/bridge-connector: Fix bridge in
   drm_connector_hdmi_audio_init()"), currently in drm/drm-fixes, not yet
   on drm-misc*

 * "drm/display: bridge-connector: correct CEC bridge pointers in
   drm_bridge_connector_init"
   (https://lore.kernel.org/lkml/20250719-fix-cec-bridges-v1-1-a60b1333c87d@oss.qualcomm.com/),
   not yet applied

[0] https://gitlab.freedesktop.org/drm/misc/kernel/-/commit/0cc6aadd7fc1e629b715ea3d1ba537ef2da95eec
[1] https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com/t/#u

Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
Luca Ceresoli (9):
      drm/display: bridge-connector: use scope-specific variable for the bridge pointer
      drm/display: bridge-connector: remove unused variable assignment
      drm/bridge: add drm_for_each_bridge_in_chain_scoped()
      drm/display: bridge-connector: use drm_for_each_bridge_in_chain_scoped()
      drm/atomic: use drm_for_each_bridge_in_chain_scoped()
      drm/bridge: use drm_for_each_bridge_in_chain_scoped()
      drm/bridge: remove drm_for_each_bridge_in_chain()
      drm/bridge: add drm_for_each_bridge_in_chain_from()
      drm/omap: use drm_for_each_bridge_in_chain_from()

 .clang-format                                  |  2 +-
 drivers/gpu/drm/display/drm_bridge_connector.c | 13 +++----
 drivers/gpu/drm/drm_atomic.c                   |  3 +-
 drivers/gpu/drm/drm_bridge.c                   |  3 +-
 drivers/gpu/drm/omapdrm/omap_encoder.c         |  4 +-
 include/drm/drm_bridge.h                       | 52 ++++++++++++++++++++++++--
 6 files changed, 58 insertions(+), 19 deletions(-)
---
base-commit: 46c366851a0b2159bdb97afcac04e5dec0cf09e8
change-id: 20250718-drm-bridge-alloc-getput-for_each_bridge-f141ae17b65a
prerequisite-change-id: 20250718-fix-cec-bridges-245d334d3712:v1
prerequisite-patch-id: df6d3d4a62c942703fab374bee85c49e4ac259cc
prerequisite-message-id: <20250620011616.118-1-kernel@...kyi.com>
prerequisite-patch-id: ba5a6a15ea02bcee387db0e92ffb4cd0e1fbf816

Best regards,
-- 
Luca Ceresoli <luca.ceresoli@...tlin.com>

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